This invention relates to the field of data processing, and, more particularly to improvements in a personal computer system and method of operating the system to provide for the real time capture, compression, and recording of motion video.
Recording of digital motion video in real time without compression produces an excessively high data rate that exceeds the file I/O transfer capabilities of many personal computer systems. A high data rate produces large files that quickly exhaust disk storage thereby reducing the length of recordings that can be made with a given amount of disk storage. While real time compression of motion video during recording can be accomplished with compression assisted by specialized hardware, a software motion video compression algorithm that executes in real time in the main processor of a personal computer is required to make motion video recording practical when low-cost video capture devices, without hardware compression, are used.
Since the computational complexity of most software-only motion video compression algorithms is too great to execute in real time, motion video recording is often performed frame-by-frame, and the image data is compressed during the capture process. While this method generally produces high quality and compression, it has the disadvantage that recording requires costlier "frame stepping" source devices such as video disks which may also entail conversion of source media. This method of recording is time consuming and precludes capture from "live" sources such as video cameras.
Real time capture can be accomplished in a software only environment by capturing raw data and transferring it to disk, compressing it later in non- real time. One drawback to such approach is that capturing raw motion video data at an acceptable resolution and frame rate results in an excessively high data rate. For example, capturing a 160.times.120 image with 16-bits per pixel at 15 frames per second, results in a raw data capture rate of 576,000 bytes per second. This data rate exceeds the available disk file I/O rate of many commonly available personal computer systems. Furthermore, motion video capture is usually accompanied by a digital audio capture which further increases the data rate. Even in systems that can sustain the required data transfer rates, the volume of data that is produced limits the length of time that can be recorded. A 200 megabyte hard disk holds only about five minutes at 576,000 bytes per second. Another drawback is that second pass compression, which is generally acceptable for capturing recorded video data, does not work for live video capture/playback applications such as video conferencing.
Specialized digital video capture adapters with hardware support for compression solve these problems by enabling real time capture with compression. However, such adapters are relatively costly and have a smaller installed base that the more common video capture adapters that do not support specialized hardware-based compression.